Thousands of posters by Hackney-based artist Stik have been stolen.
The street artist, known for painting large stick figures, arranged to distribute 100,000 prints of his 2016 work "Holding Hands" to the borough's residents.
The prints were created to celebrate the "Holding Hands" sculpture which was installed in Hoxton Square last month.
Police discovered batches of the prints were being sold online and urged anyone with information to come forward.
About 1,000 prints have since been returned, though a large amount are still unaccounted for.
Stik said the artworks were intended "as a gift to the people of Hackney". Any prints which are returned will be redistributed to those who missed out.
Det Con James Readman, of The Met Police, called for the remainder of artworks to be returned.
He said: "The artist began this project as a gift to the people of Hackney and paid a substantial amount of money out of his own pocket to meet the cost of printing.
"While some residents happily received theirs, many thousands of others were left very disappointed.
"It appears at this stage that somewhere along the supply and distribution chain, boxes containing thousands of copies of the print have been taken without permission and sold on."